The invention relates to a container, particularly for liquids, consisting of at least two coaxial parts manufactured from synthetic material and interconnected by their peripheral edges.
It is known per se to form containers of synthetic material, e.g., for liquids, from two adjoining and interconnected parts. The Netherlands Patent application 64,14980, describes a container made of plastic and constructed from two tapering parts of which the end edges are outwardly bent over and interconnected by sealing them together.
The Netherlands Patent application 72,05432 proposes a container manufactured from synthetic material and consisting of at least two parts, the two parts being interconnected by means of teeth extending along the circumference and engaging each other.
As to the manufacture of a container from synthetic material, there are only a limited number of processes which are considered.
The process which is mostly and universally followed is extrusion blow molding, wherein an extruded tube is introduced into a divisible die, which tube, after closing the die, is inflated by comprssed air, so that the still pliable tube conforms to the configuration of the die. The compressed air acts as the core of the mold form. In this way it is possible to manufacture hollow articles like vessels and containers in one piece. This process is attractive due to the comparatively moderate die cost, since, contrary to an injection molding process, the die for blow molding has no core and in fact consists only of the outer mold which moreover is not exposed to such high pressure as the injection molding dies.
This method suffers from the disadvantage that there are limitations as to the shape of the finished article, in particular the limited possibility of separately determining the wall thicknesses at various locations.
A cylindrical container with a flat bottom manufactured according to this method has the drawback that on the point of tangency of the shell with the bottom or cover, the extruded tube is more stretched than in the central part or the upper surface and lower surface, respectively.
In practice those locations, i.e., the locations at which the shell merges into the upper or lower surface, are consequently most liable to damage, and if those weak spots should be reinforced, this implies that almost the whole container should be stiffened which involves a certain waste of material.
In order to avoid this more or less excessive blow-out, the bottoms of blown containers are usually constructed in such a way that their diameter is smaller than that of the shell, whereby the surface by which it bears on the ground is not insignificantly reduced which impairs the stability when conveyed by conveyor tracks or other means of conveyance. Although attractive due to low cost of production, the blow molding process has drawbacks which may weigh heavily.
By using an injection molding method it is possible to obtain certain shapes for tube rings and bottoms which, when assembled, constitute a container which at the most damageable locations, in this case the locations at which the shell merges into the upper and lower face and at one or more locations on the circumference of the shell, is provided with reinforcements.